The present invention relates generally to a method and system of water electrolysis, and more particularly to a method and system of water electrolysis employing external gas-lift for water circulation.
Water electrolysis systems quite frequently employ some mechanical means for circulating water. The process has the advantage of controlling the temperature while at the same time ensuring an adequate supply of reactantxe2x80x94i.e., waterxe2x80x94to the electrodes. Forced circulation is acceptable for most applications. For the applications that could benefit in some way from a reduction in the number of system parts, other designs have been implemented. For example, static water feed electrolysis cells use a semi-permeable membrane next to the electrode to separate bulk water from the amount needed for the process. Each cell contains the semipermeable membrane and additional manifolds to handle, what amounts to, an additional fluid stream. The cell design is therefore more complex. Temperature control is achieved by some other means. Cells of this design have been tested successfully, but have the disadvantage of higher power consumption for the same gas output, i.e., current density.
There is a need for a water electrolysis method and system that preserves the cell performance over a wide range of current densities without the added complexity of a mechanical device for water circulation so as to extend the field of potential applications.
Other objects and advantages of this invention will become more readily apparent when the following description is read in conjunction with the accompanying drawings.
In one aspect of the present invention, a water electrolysis system includes a water electrolysis cell stack having an anode and a cathode. A water storage tank having an outlet is disposed above the cell stack and communicates with an inlet of one of the anode and the cathode of the cell stack for gravity feeding water from the water storage tank to the cell stack. A phase separator is disposed below and in communication with the water storage tank. The phase separator has an inlet for receiving a two phase stream including water and product gas exiting an outlet of the one of the anode and cathode of the cell stack, and includes a conduit having a lower end disposed within the phase separator for receiving water recovered in the phase separator. The conduit has an upper end extending into the water storage tank. Further, the conduit defines a plurality of openings along a portion of the conduit disposed in the phase separator such that the product gas received in the inlet of the phase separator enters the inside of the conduit through the openings and entrains and lifts water upwardly therewith through the conduit and into the water storage tank, whereby water may be recirculated through the stack. This lifting of water entrained on gas bubbles is known as the gas lift principle. Preferably the system operates in an anode feed mode whereby water is circulated by means of the gas lift principle through the anode side of the cell stack, and the product gas providing gas lift is oxygen.
In another aspect of the present invention, a method of circulating water through a water electrolysis cell stack having an anode and a cathode includes gravity feeding water from a water storage tank to an inlet of one of the anode and cathode of the cell stack. A two phase stream including water and product gas is separated upon the two phase stream exiting an outlet of the one of the anode and cathode of the cell stack. The separated water is directed upwardly into the water storage tank for recirculation through the cell stack by means of the gas-lift principle where bubbles of product gas in the water entrain water and move the entrained water upwardly along with the bubbles so that the recovered water may be in position to be recirculated through the cell stack.